Most of the loads, coupled to a general alternating current distribution system, comprise resistive and inductive components, except the purely resistive loads such as an incandescent lamp or an electric stove. Therefore, the current phase angle of electric lines will lag behind the voltage. Generally, The total current, supplied through power transmission lines and distribution lines by a power company's generator, can be resolved into an active current part and a reactive current part according to the rated voltage of each load. The kilowatt-hour meter in the user end only records the active power. However, the reactive power will incur a line drop and a line loss. It's the loss both for the power company and the user. Consequently, how to accomplish a power-factor regulation is to be a subject, which the manufacturers of the user end systems desire to develop.
The technology of the power-factor regulation can be categorized into an active type and a passive type. The advantages of utilizing the power-factor regulation include reducing power loss, increasing load life and saving power expenditure. The power-factor is usually improved via a capacitor. The current power supply industry usually adopts a power-factor regulator to achieve the effect of outputting a stabilized voltage. Referring to FIG. 1, after a modification, the waveform of the working voltage of an inverter tends to be a ripple wave. However, in some part of the industry, this mode will incur troubles, which will be described below.
The output power of an inverter of a piezoelectric-transformer type is determined according to an input voltage. For the current power supplies, the output voltage is usually a smaller one, such as a stable 24 V or 48 V; therefore the output power of the inverter of the piezoelectric-transformer type is reduced responsively. The inverter of the piezoelectric-transformer type utilizes a piezoelectric effect induced by the mechanical stress of the vibration of piezoelectric sheets.
In the conventional method, when a power is supplied, the piezoelectric sheets have to maintain to operate at the voltage of 48V. As the piezoelectric sheets operate under the vibration induced by a single highest voltage in the conventional method, the life of the inverter of the piezoelectric-transformer type is apt to be reduced.